Layers porosity

Unfortunately, cell performance is not proportional to catalyst layer porosity. In order to achieve maximum fuel cell performance, the CL should have an optimal porosity [24]. With higher catalyst layer porosity, the mass transfer rate increases, while the electron and proton transport rates decrease. Gamburzev and Appleby [25] documented fuel cell performance with pore formers in the CL and found that optimum pore-former content was about 33%. 

Up to 48 ternary catalyst mixtures were prepared simultaneously in less than 1 h. Hence the sputtering procedure is much faster than the wet chemical route and in fact one of the fastest syntheses available. This advantage is gained at the expense of low layer porosity. Thus, sputtered catalysts are new artificial catalysts and not directly comparable to catalysts prepared by wet-chemical procedures. These catalysts offer the advantage of quick preparation and characterization compared with alumina-based catalysts. They can also be used for obtaining so-called intrinsic kinetics because there is no influence of diffusion. 

Layer density and elastic properties primarily determine the speed or velocity at which sound will travel through the layer. Porosity, mineral composition, and water content of the layer affect density and elasticity. 

AHSTRACT Modelling and computing of thermal biomass treatment processes involving thick layers requires that the gas permeability and hydraulic resistance of such layers be known. The paper presents the results of experimental research into the hydraulic resistance of the thick layer comprised of two biomass varieties sunflower husks and sawdust. The research was conducted within the range of Re alteration from 5-70, and layer porosity change 0.2-0.7,... 

Porosity is greatly determined by the particle shape. Ball shape allows for the minimum void volume in an irregular filling. However, the layer porosity characteristics obtained for the simplest case of ball-shaped evenly-sized particles cannot be applied for determining the type of the filling, or the shape of the channels formed by the particles and, consequently, for estimating the layer resistance... 

The layer porosity is inversely proportional to the water vapor concentration and average grain size (diffusion rate). 

The pressure losses of electric separators in comparison with the other types are very low, ranging between 60 and 250 Pa. A good separation efficiency with saving optimum operation conditions may be achieved in mechanical dry separators as well as wet separators at pressure losses of 600 to 1200 Pa (except for Venturi and slot separators). Considerable pressure losses occur in the filtration layer. Their values depend on the layer porosity , diameter of filtration material fibres, layer thickness, gas dynamic viscosity and the velocity of the streaming gas. 

With the increase of FGM layer porosity P, the change of stress at the bonding interface of the three-layered plate increases, and the stress curves appear peak values. The tensile stress on the surface of ceramics reaches the maximum. The tensile stress is unfavorable to the strength of ceramics. 

Yan, W.M., et al.. Effects offlow distributor geometry and diffusion layer porosity on reactant gas transport and performance of proton exchange membrane fuel cells. Journal of Power Sources, 2004.125(1) pp. 27-39. 

The coating stability, essentially related to the preparation process, usually decreases with thickness and layer porosity. 

The cathode of a modem Ni-Cd battery consists of controlled particle size spherical NiO(OH)2 particles, mixed with a conductive additive (Zn or acetylene black) and binder and pressed onto a Ni-foam current collector. Nickel hydroxide cathode kinetics is determined by a sohd state proton insertion reaction (Huggins et al. [1994]). Its impedance can therefore be treated as that of intercalation material, e.g. considering H+ diffusion toward the center of sohd-state particles and specific conductivity of the porous material itself. The porous nature of the electrode can be accounted for by using the transmission line model (D.D. Macdonald et al. [1990]). The equivalent circuit considering both diffusion within particles and layer porosity is given in Figure 4.5.9. Using the diffusion equations derived for spherical boundary conditions, as in Eq. (30), appears most appropriate. 

Note that the values of HETP decrease, first with decrease of the radius of capillary column and, secondly, with increase of adsorption layer porosity. 

Among many other microstructural parameters, porosity is one such physical parameter, which is generally used to describe the degree of porous nature of a PS layer. Porosity has been well researched with the fabrication methods and environment. Therefore, if this physical parameter could be correlated with electrical conductivity of the PS using any analytical way, it could serve an important role in tailoring the microstructure to obtain desired device properties. However, not much work has been done to explore this correlation. Effective medium approximation (EMA) as proposed by Bruggeman was used to some extent to determine a correlation between the effective conductivity of the PS layer and porosity of the layer ... 

This approach, developed by Fauchet, Striemer, and coworkers, creates mesoporosity via thermal anneal treatments of ultrathin (10-50 nm) silicon films (Fang et al. 2010). A typical process flow is shown schematically in Fig. 2. For silicon Aims sandwiched between silica layers, porosities up to 15 % were achieved. The potential in vitro and in vivo biomedical uses of such membranes are reviewed in the handbook chapter Porous Silicon in Immunoisolation and Biofiltration. Very recently, higher levels of porosity have been achieved using silicon nitride rather than oxide as the barrier layers (Qi et al. 2014). 

In relation with the functional properties of a part, such as fatigue and static strength, or wear and corrosion resistance, are the basis for specifying the proper process and steel as illustrated in Fig. 2 (T. Bell, 2005). The functional part properties that essentially depend on the compound layer are wear resistance, tribological properties, corrosion resistance and general surface appearance. Both abrasive and adhesive wear resistance increase with hardness and with minimised porosity of the compound layer. Porosity can be positive in lubricated machinery parts as the pores act as lubricant reservoirs. The compound layer depth has to be deep enough not to be worn away. The diffusion layer (depth, hardness and residual stress) determines surface fatigue resistance and resistance to surface contact loads. 

Catalyst layer porosity, where very small pores can prevent freezing due to freezing point depression. 

We discussed in this chapter about the limitations of the simplified model for determination of limiting current density based on the gas-phase diffusivity. In particular, besides the diffusion media, there is also diffusion resistance in the catalyst layer, which is in series with the gas diffusion layer, and the effects of a thin Nafion or liquid layer on the catalyst. Assume the anode and cathode catalyst layer porosity is 0.5 and thickness is 20 nm. Consider a system with a thin layer of flooding and an ionomer on the catalyst. Consider the cathode only, at a normal operating temperature of 80°C, and a pressure of 15 psig. Assume the average mole fraction of the oxygen in the flow channel 0.12. Develop an expression for, and solve for, the mass... 

Yan, W. M., C. Y. Soong, F. L. Chen, and H. S. Chu, Effects of Flow Distributor Geometry and Diffusion Layer Porosity on Reactant Gas Transport and Performance of Proton Exchange Membrane Fuel Cells, Journal of Power Sources, Vol. 125, 2004, p. 27. 

---